Evaluation of the dosimetric accuracy of HyperSight CBCT for CBCT-only adaptive radiotherapy workflow

This study evaluates the dosimetric performance of HyperSight CBCT (HS-CBCT) images for CBCT-only adaptive radiotherapy workflows.

We evaluated Hounsfield unit (HU) accuracy and dose calculation performance using both Feldkamp-Davis-Kress (FDK) and Acuros reconstructions in phantom and clinical datasets (brain, breast, pelvis). HU deviations were reported relative to planning CT. Longitudinal HU stability was assessed over 20 CBCT sessions in a prostate cohort. Gamma passing rates (2 %/2mm) were used for dosimetric evaluation.

Acuros-reconstructed CBCT images demonstrated HU agreement within 28 HU of the planning CT, compared to deviations up to 284 HU for FDK (the relative coefficient of variation -CV- of the difference from the pCT reference value were 2 % and 20 % for Acuros and FDK respectively). Dose recalculations on Acuros images resulted in higher gamma passing rates, particularly in pelvic cases (97.8 % vs 96.6 % with FDK, p < 0.05). HU stability analysis over 20 CBCT sessions in prostate patients confirmed reproducibility, with standard deviations of 5.0 HU for bone and 4.2 HU for bladder.

This study provides the first comprehensive, multi-site and longitudinal clinical validation of HyperSight CBCT with Acuros reconstruction for ART workflows. Our results demonstrate high HU fidelity and robust dose calculation performance, supporting the clinical feasibility of CBCT-only workflows across different anatomical regions and throughout the course of treatment.